There has been known a technology for the near-field wireless communication, the communicable distance of which is from several meters to several tens of meters. For example, Wireless USB (Wireless USB Specification Revision 1.0) targets at a communication distance of about 10 meters. The Wireless USB assumes that a transmission rate is 480 Mbit/s at the communication distance of 3 meters, and that the transmission rate is 110 Mbit/s at the communication distance of 10 meters.
The Wireless USB adopts UWB (ultra Wide Band) as a wireless platform at a physical layer. The UWB uses a wide band from 3.1 GHz to 10.6 GHz, and achieves a transmission rate of several hundred Mbit/s or higher at a short distance within a 20 meter radius. As modulation methods for the UWB, there have been proposed an impulse wireless method, an MB-OFDM (MultiBand-Orthogonal Frequency Division Multiplexing) method, a DS (Direct Sequence)-UWB method for performing a direct spreading by PSK modulation, and the like. Communication devices using the MB-OFDM UWB method are disclosed in e.g. Patent Literatures 1 and 2. A communication device using the impulse wireless method is disclosed in e.g. Patent Literature 3.
Recently, there has been also proposed a wireless communication method where the communicable distance is confined to a near area of about several centimeters. For example, TransferJet is a wideband wireless communication method where a near area within 3 centimeters is assumed as the communicable distance. According to a statement issued by TransferJet consortium proposing the TransferJet (http://www.transferjet.org/en/index.html), the TransferJet uses a microwave band (central frequency 4.48 GHz). The average transmitted power is equal to or lower than −70 dBm/MHz, and the maximum transmission rate is 560 Mbit/s at the communication distance within 3 centimeters.